Structural characterization of poly(diethylsiloxane) in the crystalline, liquid crystalline and isotropic phases by solid‐state ¹⁷O NMR spectroscopy and ab initio MO calculations

Abstract

The structure of poly(diethylsiloxane) (PDES) has been characterized using solid-state NMR of (17)O. The sample studied had a weight-average molecular weight of 2.45 x 10(5). The sample was prepared by utilizing the cationic ring-opening polymerization of (17)O-enriched hexacyclotrisiloxane. Solid-state NMR of (17)O-enriched PDES was measured on the low-temperature beta(1) phase, the high-temperature beta(2) phase, the two-phase system consisting of the liquid crystal and isotropic liquid phase and the isotropic phase. From these data, the molecular structure and dynamics of PDES in the various phases were characterized via the chemical shifts of (17)O, and electric field gradient parameters were determined from NMR and ab initio molecular orbital (MO) calculations. In addition to the solid-state NMR of (1)H, (13)C and (29)Si previously reported on these samples, knowledge of the dynamic behavior of PDES as inferred from the NMR of (17)O in the present study was enhanced significantly. Further, the potential of combining the experimental NMR of (17)O with ab initio MO calculations to characterize the dynamics of polymers containing oxygen is demonstrated.

Influence of N−H···O and C−H···O Hydrogen Bonds on the 17O NMR Tensors in Crystalline Uracil: Computational Study

“…A number of recent solid-state 17 O NMR studies have accumulated a considerable amount of experimental data on the tensorial aspect of the 17 O NMR parameters. [2][3][4][5][6][7][8][9][10][11][12][13][14] In parallel to experimental studies, attention has also been paid to theoretical prediction of 17 O NMR tensors. 12,13,[15][16][17][18][19][20] The purpose of performing first-principle calculations on 17 O NMR tensors is not only to check the validity of computational methodology, but also to provide a useful tool for interpreting experimental NMR data in relation to HB interaction, molecular structure, and dynamics.…”

“…We thank Dr. Hartmut Schmider of HPCVL for technical assistance. R.I. is grateful to Queen's University for an R. S. McLaughlin Fellowship (2004-2005. We also thank Ms. Kathy Xu for assistance in preparing the manuscript.…”

Wobbling and Hopping: Studying Dynamics of CO2 Adsorbed in Metal–Organic Frameworks via 17O Solid-State NMR

“…CO 2 dynamics in MOFs are typically studied via 13 C solid-state NMR (SSNMR) experiments using 13 C-enriched 13 CO 2 gas. − 13 C is a spin-1/2 nucleus associated with relatively narrow static SSNMR powder patterns that exhibit lineshapes dominated by the anisotropic chemical shift (CS) interaction, which is sensitive to the local environment and dynamics. 17 O SSNMR experiments are often used for characterization of oxides, glasses, and biomolecules. − 17 O SSNMR experiments are also a sensitive probe of dynamics, but are rarely used for this purpose. − 17 O has a spin of 5/2, a nuclear quadrupole moment of −25.6 mb, and a low natural abundance (0.037%) that usually requires isotopic enrichment. The quadrupolar interaction (QI) with the local electric field gradient (EFG) often gives rise to broad SSNMR spectra of low signal-to-noise ratios (S/N) that demand long experimental times; however, the QI is also sensitive to local structure and dynamics.…”

Solid state NMR spectroscopy

“…564 Structural characterisation of poly(dimethylsiloxane) was achieved using 17 O MAS NMR spectroscopy. 565 1 H and 29 Si NMR data were used to determine the structure of a poly(dimethylsiloxane) layer at the surface of hydrophilic SiO 2 . 566 29 Si CP/MAS NMR spectra were used to characterise poly(aminopropyl/phenyl)silsesquioxane.…”

“…829 Solid-state 17 O NMR data probed the structure and dynamics of poly(diethylsiloxane) in b 1 and b 2 liquid crystal phases. 830 Solid-state 2 H NMR spectra were used to determine the motion of NH 4 + ions in feldspar, N(D/H) 4 AlSi 3 O 8 . 831 A 31 P NMR study has been reported for spin-dynamics in Si:P. 832 1 H and 31 P spin pairs in solid SnHPO 3 and SnHPO 4 gave information on spindynamics in these systems.…”